The invention relates generally to plasma chambers used in processes for manufacturing semiconductors and other electronic devices. More specifically, the invention relates to apparatus and methods for preventing plasma within the chamber from extending through the exhaust passage or exhaust channel that couples the chamber to an exhaust pump.
The series of process steps used to fabricate semiconductors and other electronic devices commonly include various plasma processes for depositing or etching films. Such plasma processes generally are performed within a vacuum chamber whose interior is maintained at a low pressure by an exhaust pump. The pump is coupled to the chamber interior via an exhaust channel.
There are several reasons that is important to prevent the plasma within the chamber from extending through the exhaust channel to the exhaust pump.
One reason is that a plasma that extends a considerable distance through the exhaust channel typically is unstable, which causes the main plasma body adjacent the workpiece to be unstable, as evidenced by visible flickering of the light emitted by the plasma. Such instability produces unacceptable non-uniformities in the plasma process.
A second reason it is important to block the plasma from extending to the exhaust pump is to protect the pump from corrosion or undesirable deposits. Any component surfaces near the plasma body within a plasma chamber generally will be corroded due to bombardment by ions from the plasma. In addition, many plasma processes have byproducts which include reactive species that can combine to form polymers or other undesirable deposits on components within the chamber that are adjacent to the plasma body. To prevent such corrosion and undesirable deposits, it is common practice to cover with removable liners the surfaces of chamber components that are exposed to or adjacent to the plasma body. The liners are replaced periodically as they become corroded.
Typically it is impractical to provide easily replaceable components for the exhaust pump. Therefore, a need exists for a plasma chamber design that prevents the plasma within the chamber from extending too close to the exhaust pump.
Commonly assigned U.S. Pat. No. 5,891,350, issued Apr. 6, 1999 to Shan et al., discloses a plasma chamber design that prevents the plasma from reaching the exhaust pump by interposing a long and sinuous exhaust passage between the chamber interior and the pump. One disadvantage of this design is that the sinuous exhaust passage creates a pressure drop between the chamber interior and the pump. In some applications, this may require an overly expensive pump to achieve a desired low chamber pressure.
The invention concerns a plasma reactor employing a chamber enclosure including a process gas inlet and defining a plasma processing region. A workpiece support pedestal capable of supporting a workpiece at processing location faces the plasma processing region, the pedestal and enclosure being spaced from one another to define a pumping annulus therebetween having facing walls in order to permit the process of gas to be evacuated therethrough from the process region. A pair of opposing plasma confinement magnetic poles within one of the facing walls of the annulus, the opposing magnetic poles being axially displaced from one another. The magnetic poles are axially displaced below the processing location by a distance which exceeds a substantial fraction of a spacing between the facing walls of the annulus.
The invention further concerns a chamber enclosure having a process gas inlet and defining a plasma processing region. A workpiece support pedestal capable of supporting a workpiece at processing location facing the plasma processing region, the pedestal and enclosure being spaced from one another to define a pumping annulus therebetween having facing walls, to permit process gas to be evacuated therethrough from the process region. A pair of opposing plasma confinement magnetic poles within one of the facing walls of the annulus, the opposing magnetic poles being axially displaced from one another. The magnetic poles are axially displaced below the processing location by a distance which is sufficient so that the magnetic field adjacent the workpiece plane is on the order of about 50 times less than the magnetic field across the annulus adjacent the magnetic poles.